JPS61112940A - Apparatus for measuring base material of optical fiber - Google Patents

Abstract

PURPOSE:To provide the titled measuring apparatus for measuring or inspecting various measuring factors of the base material of an optical fiber in an extreme ly efficient manner, by using existing measuring apparatuses and organically the same. CONSTITUTION:The base material of an optical fiber is attached to specimen rotating drive apparatuses 4, 6 and an illumination apparatus 8 is subsequently energized to allow sufficiently excited light to irradiate the incident terminal 2a of the base material 2. The transmitted light intensity distribution (near field pattern) corresponding to refractive index distribution is measured at the emitting terminal 2b of said base material 2. The reception of light intensity is performed by using a terminal surface light intensity detection apparatus 26 such as a TV camera and a core/clad diameter ratio is measured simultaneously with the measurement of refractive index distribution. Further, in order to measure an internal flaw, the specimen rotating drive apparatuses 4, 6 are operated to rotate the base material 2 at a predetermined rotary speed and, at the same time, a weak light detection apparatus 32 is operated while moved along the longitudinal axis direction of the base material 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inspection device for an optical fiber preform (base material), and more specifically, for measuring the refractive index distribution of an optical fiber preform, measuring the core and cladding diameters, The present invention also relates to a comprehensive inspection device for optical fiber preforms that can measure defects within the preform simultaneously and in a short time.

BACKGROUND OF THE INVENTION With the development of optical communication systems, it has been desired to manufacture large quantities of communication optical fibers of particularly high quality and precision. Optical fibers are manufactured by first making a preform (base material) with a diameter of ~5σ using various methods such as a CVD method, an external CVD method, a plasma CVD method, and a vapor phase attachment method. Manufactured by heating and drawing the base material. The shape and structure of the optical fiber are drawn almost exactly similar to the shape and structure of the base material before drawing, and the refractive index (in the radial direction) on the cross section is an extremely important characteristic for optical fibers. The distribution is also exactly similar between the optical fiber and the matrix since the thermal diffusion of the dopant during the drawing process is very minimal.

Therefore, in order to obtain a high-quality, highly precise optical fiber, it is essential to first manufacture an optical fiber preform having the desired shape, structure, and refractive index distribution. The base material is rigorously measured and inspected.

As understood from the above, the factors of the optical fiber base material that have a very large effect on the performance of the optical fiber are the distribution of refractive index in the tllll generatrix cross section, (2) core/cladding diameter ratio, and (3) matrix. Defects within the material, primarily pores within the matrix, are factors that are measured or inspected.

Conventionally, the distribution factor (1), that is, the refractive index distribution of the base material, has been determined using a preform analyzer or an interference microscope. Measurement with a preform analyzer uses interferometry, focusing method, etc. to measure the refractive index distribution, and the measurement accuracy is 14 high, but it is generally used for point measurements.
-It took a considerable amount of time to measure the base material, requiring measurements at hundreds or thousands of points. This method, which used a preform analyzer, required the use of a matching liquid, which required liquid sealing and liquid removal operations, making the operation extremely complicated.

Furthermore, when using an interference microscope, there is an advantage that the substance of the refractive index distribution can be directly observed, but it is essential to slice the optical fiber base material and polish both sides, and it is difficult to prepare such a sample. It took a considerable amount of time. As described above, this method is a destructive testing method, and from this point of view as well, it cannot be said to be a suitable measurement method.

Furthermore, this method using an interference microscope has the disadvantage that interference fringes are measured by visual inspection, and many human errors are included.

The core/clad ratio, which is another measurement factor for optical fiber preforms, is determined by the fact that the preform analyzer and interference microscope use a matching liquid, which virtually eliminates the cladding. It is not possible to measure the refractive index distribution using a microscope at the same time, and the measurement must be performed separately using another microscope.

Furthermore, inspection for internal defects in other optical fiber base materials has conventionally been carried out by entering light from one end of the base material and visually observing the scattered light at the defective part, but this method can detect large defects. However, it is difficult to detect micropores and to inspect the influence of the micropores on the fiber after drawing.

As mentioned above, conventional methods and devices for measuring optical fiber preforms are still not sufficient in terms of the time required for measurement, measurement accuracy, and sample preparation. It was not possible to test.

Therefore, an object of the present invention is to provide an optical fiber preform measuring device that can measure or inspect various important measurement filters of an optical fiber preform in a short time and with high accuracy.

-5 Another object of the present invention is to provide a refractive index distribution of an optical fiber preform;
An object of the present invention is to provide an optical fiber preform measuring device capable of simultaneously measuring or inspecting the core/cladding diameter ratio and internal defects.

Another object of the present invention is that existing measuring devices can be used and by organically combining such devices various measurement factors of optical fiber preforms can be very efficiently measured or tested. An object of the present invention is to provide an optical fiber base material measuring device.

Next, the optical fiber preform measuring device according to the present invention will be explained in detail with reference to the drawings.

Referring to FIG. 1, an embodiment of the overall configuration of an optical fiber preform measuring device according to the present invention is schematically illustrated. In principle, this measurement device allows incoherent light to be incident on one end of an optical fiber base material, and when all propagation modes are excited uniformly, the light intensity at the other end of the optical fiber base material, that is, at the output end. When the refractive index distribution of an optical fiber base material is measured using the fact that the distribution is similar to the refractive index distribution, a so-called near-field pattern method (NFP method) is employed. However, the NFP method applied to the present invention is significantly different from the NFP method conventionally used for measuring optical fibers. That is,
The problem is that the excitation fiber system used in the NFP method for optical fibers cannot be used. Comparing the optical fiber and the base material, the diameter/total length ratio of the sample to be measured is 5 x 10'.
In the case of the base material, the total length is short compared to the diameter, so an exciter like an excitation fiber cannot be used, so the light source itself must be able to excite sufficiently uniformly.

The optical fiber preform measuring device 1 includes sample rotation drive devices 4 and 6 that rotatably hold an optical fiber preform 2 manufactured by any method at both ends thereof. The sample rotation drive devices 4 and 6 are arranged at a predetermined interval, and can detachably hold the optical fiber preform between them, and rotate the preform 2 at a predetermined number of rotations as desired. As much as possible
One of the drive devices is provided with a drive source.

To explain in more detail, the sample rotation drive devices 4 and 6 are as follows:
It is a rotary drive device of a variable rotation speed type, and in particular, the sample rotation drive device 6 has a function of being able to move in the horizontal direction according to the length of the base material.

As seen in FIG. 1, the left end 2a of the optical fiber preform 2 protrudes slightly further to the left from the end surface of the sample rotation drive device 4, and is used as the entrance end in this embodiment. A light source device 8 is provided facing the incident end 2a. The device 8 is
The light source must be able to irradiate the entire input end of the optical fiber preform and uniformly excite all propagation modes of the preform, that is, it must be sufficiently excited. Preferably, the device 8 is configured such that its output can be adjusted.

FIG. 2 schematically shows a preferred embodiment of the light source device 8. As shown in FIG. The light source device 8 includes a light source 10 such as a logen lamp.
has. A reflecting plate 12 is disposed on the back of the light source 10, that is, on the left side in FIG. 2, and directs the light rays from the light source 10 as parallel rays to the front, that is, on the right side in FIG. A whitening filter 14 is arranged in front of the light source 10 to produce a sufficiently excited light beam. A condenser lens 16, a parallel lens 18, and a condenser lens 20 are arranged in front of the whitening filter 14, and the light beam from the light source 10 is directed to the optical fiber preform 2.
It is configured to irradiate the entire incident end 2a of. The condensing lens 20 has an angle α of the incident light ray that is similar to the optical fiber base material 2.
It is movable back and forth in order to adjust the aperture angle to be larger than that of the opening angle. Further, a filter holder 22 can be provided between the parallel lens 18 and the condensing lens 20 so that a filter can be inserted as desired.

Although the light source 10 has been described as a halogen lamp in the above description, the wavelength of the light beam output from the light source device 8 may be visible white, or may be a single infrared wavelength.

The various optical system elements described above are preferably arranged within the light source device housing 24.

On the other hand, the other end 2b of the optical fiber preform 2 is the output end in this embodiment, and slightly protrudes further to the right from the end surface of the sample rotation drive device 6. An end face light intensity detection device 26, for example, a TV right camera, is provided facing the output end 2b and adjustable to maintain a predetermined distance from the output end 2b. The TV right camera 6 may be a normal one available on the market, and may be, for example, an imaging camera for measuring light intensity distribution. Moreover, the edge light intensity detection device 26
It is also possible to use a simple light intensity meter as long as it can be driven arbitrarily in the radial direction.

In this measuring device, in order to improve the accuracy of measuring the radial refractive index distribution of the optical fiber preform 2,
A cladding mode absorbing means 30 is provided on the incident end side of the cladding mode absorbing means 30 . Usually, the cladding mode absorption means 30 is a device that applies a matching liquid around the optical fiber base material 2 and holds it, but it is constituted by a band made of a material with a higher refractive index than the cladding layer. You can also do that. Therefore, it can be made of a resin with a high refractive index, such as silicone resin.

The cladding mode absorbing means 30 made of resin is simply attached to the appropriate position on the input end side of the optical fiber base material 20 after applying the matching liquid.
It has the advantage of being extremely easy to handle.

Furthermore, this measuring device is provided with a weak light, that is, a radial light detection device 32 for inspecting internal defects in the optical fiber preform 2. The weak light detection device 32 is a high-performance light intensity meter that can detect weak leakage light scattered by internal defects, especially pore formation parts, and scattered to the outside of the optical fiber preform 2.

Preferably, such a light intensity meter is, for example, a light intensity meter for measuring the intensity of light propagating in the air.

A detector 34 of the weak light detector 32 is mounted on a gear rear 36 and is movable in the longitudinal direction of the optical fiber preform 2. The carrier 361d may be of the type that runs on a track (not shown) or may be of any other suitable means.

Since the light-receiving section used for internal defect inspection is highly sensitive even to weak light, the inside of the apparatus main body is kept in a dark room by a light-shielding cover shown at 100.

Next, the operation of the optical fiber preform measuring device 1 configured as described above will be explained.

The optical fiber base material 2 is attached to the sample rotation drive devices 4 and 6 in a double series, and then the illumination device 8 is energized to irradiate the incident end 2a of the base material 2 with a sufficiently excited light beam. . By this light irradiation, the light is propagated to the other end of the base material 2, and the transmitted light intensity distribution corresponds to the refractive index distribution (Afield pattern).
is observed at the output end 2b. The light intensity distribution is received by an edge light intensity detection device 26 such as a TV right camera, transmitted to an image processing device 40, and displayed on a monitor CRT 42, and the measurement results are outputted by a printer 44 as necessary. Ru.

In such a refractive index distribution measurement, the cladding mode (light propagating through the cladding layer of the optical fiber base material) that degrades measurement accuracy is absorbed by the cladding mode absorption means 30. The time required for refractive index distribution measurement with this device is approximately 2 minutes.

The core/cladding diameter ratio is measured simultaneously with the above refractive index distribution measurement. In this measurement, it is not possible to directly determine the absolute values of the core diameter and cladding diameter, or the relative value of both dimensions, that is, the core/cladding diameter ratio, can be measured within the refractive index distribution measurement time. An accuracy of 0.05% can be obtained.

To measure internal defects in the optical fiber preform 2, the sample rotation drive devices 4 and 6 are activated to rotate the preform 2 at a predetermined rotation speed.
For example, it is rotated by 100 r, p, m, and at the same time, the weak light detection device 32 is moved in the longitudinal axis direction of the base material 2 from one end side of the base material 2, from the left side to the other end, that is, to the right side in FIG. (For example, for 10 to 20 minutes.) Operate it from time to time. The output of the detection device 32 is sent to an amplifier 46 and the measurement results are recorded on a monitor recorder 48. The measurement range of the weak light detection device 32, that is, the movement range of the carrier 36, is controlled by a limit switch 50.52%. In particular, the limit switch 52 is appropriately arranged according to the length of the base material 2.

The weak light detection device 32 is capable of measuring scattered light of 50 dB (based on 1 mW) or more, and can also detect micropores in the optical fiber base material.

The time required for such a measurement is approximately 4 degrees.

The above devices in this measuring device are controlled by an arithmetic processing unit 56 equipped with a control panel board 54. It will also be appreciated that the apparatus is operated in a semi-dark room.

Since the optical fiber preform measuring device according to the present invention is configured as described above, it is possible to measure the refractive index distribution, core/cladding diameter ratio, and internal defects of the optical fiber preform with high precision and in an extremely short time. It has the advantage of being easy to operate and easy to operate. Furthermore, the device of the present invention in principle has N
Since it uses the FP method and is a non-destructive testing method, there is no problem such as wasting a large amount of time for sample preparation. Further, in this device, when a silicone resin band is used as the cladding mode absorbing means, operations such as liquid sealing and liquid removal of the matching liquid can be avoided.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of an optical fiber preform measuring device according to the present invention. Fig. 2 shows the optical fiber preform measuring device of the present invention including: 1. Optical fiber preform measuring device 2. Optical fiber preform 4.6. Sample rotation 1 drive device 8. Light source device 26. End face light intensity detection. Device 30: Cladding mode absorption means 34, weak light detection device Applicant: TAC Electric Cable Co., Ltd. Agent: Kazuhide Okada, patent attorney

Claims (4)

[Claims] (1) A sample rotation drive device for rotatably supporting the optical fiber preform, and a light source for irradiating a sufficiently excited light beam onto one end surface of the optical fiber preform held by the sample rotation drive device. an end face light intensity detection device provided adjacent to the other end face of the optical fiber preform, and an end face light intensity detection device provided covering a part of the preform at a predetermined position in the longitudinal direction of the optical fiber preform. cladding mode absorbing means, a weak light detection device that moves along the longitudinal direction of the optical fiber preform and detects scattered light from the preform, and controls the operation of the above devices and detects the measurement results. 1. An optical fiber preform measuring device characterized by comprising: means for outputting. (2) The device according to claim 1, wherein the cladding mode absorption means is a silicone resin band attached to the outer periphery of the optical fiber preform. (3) The device according to claim 1, wherein the end face light intensity detection device is a TV camera. (4) The device according to claim 1, wherein the end face light intensity detection device is a light intensity meter that is moved in the radial direction of the optical fiber.